The invention relates to hand-operated switches for repetitively activating large industrial equipment such as power presses, molding machines, riveting machines and the like. The invention is more specifically related to a photoelectric switch wherein an infrared light beam may be broken by the hand to activate a mechanical relay to thereby energize the associated machinery. More specifically, the invention is directed toward providing a switch that prevents inadvertent passage of the operator's hand past the light beam and also monitoring circuitry for detecting the failure of primary components of the system and disabling the relay circuitry from accidental operation.
It is known in the art to provide for an infrared photoelectric switch in replacement of conventional palm buttons or other manually operable switches used for activation of heavy machinery. For example, with the use of power presses or riveting machines, cycling of the machine is repeated on successive work pieces, or onto a continuous fed line of work stock, to perform a mechanical function at regular intervals. Sometimes, the operator positions the work piece with the machine and then activates the equipment to perform a mechanical procedure. Otherwise, mechanical feed means may supply the work piece, such as sheet metal to be bent or riveted, automatically to the machine, whereupon detecting the proper positioning of the work piece, the operator energizes the equipment by means of the switch. The previously used palm buttons, push buttons, and mechanical lever switches, have resulted in employee hand and arm injuries, including tendonitis, muscle strain and ligament damage. These have therefore been typically replaced by the use of photoelectric sensor switches wherein typically a light beam is transmitted from a diode to an infrared phototransistor. By interrupting the light beam, a mechanical contact closure results and a mechanical relay is activated for energizing the associated power press molding machine, etc.
While the use of photoelectric switches is generally known, problems have resulted in the poor structural configuration of the prior art switch boxes. Often, prior art devices have used infrared light beams passing across a channeled switch box for the insertion therein of the operator's hand. Most commonly, the configuration of the light beam within the channel allows for the unintentional passage of the operator's finger, or fingers, through and past the beam whereby the beam is re-established across the channel as the finger(s) inadvertently move therepast. This may not be detected by the operator and causes a dangerous situation when the operator removes his finger(s) outwardly of the channel and breaks the light beam again for an unintentional and potentially injurious re-activation of the machinery. Some rudimentary cures for this defect involve operators on-site making finger blocking devices in the beam-interrupt area of the switches to prevent passage of the hand past the light beam. Other manufacturers of photoelectric switches have provided for double infrared beams that might require either or both to be broken to activate the mechanical relay for the machinery. Problems of the same nature have arisen in these types switches also.
Another concern in the industry is the capability of mounting photoelectric switch boxes in replacement of palm-buttons on existing equipment. Special brackets and mounts have been needed to fit the switch to the electric connection boxes on the machinery. It would therefore be desirable to provide for a photoelectric switch and relay system that overcomes the foregoing problems including the capability of attachment to existing machinery without the need for special mechanical adaptors or attachments.
A further object of the invention would be to provide for a photoelectric switch and relay system wherein the electrical circuitry contained within the switch box provides a fail-safe, disabling monitor circuitry for monitoring key components of the circuit to detect failure. Such failure is quite common due to the constant on-off activation and the continuous operation of, for example, an infrared light emitting diode projecting a beam to an infrared phototransistor. It is therefore a goal of the invention to provide a primary function circuit for operating a mechanical press relay by the interruption of a light beam in combination with a disabling backup circuitry for providing a fail-safe provision for at least two of the main operable circuit components of the primary circuit.